When injecting IPIs to a set of harts, the IMSIC IPI support will
do a separate MMIO write to SETIPNUM_LE register of each target
hart. This means on a platform where IMSIC is trap-n-emulated,
there will be N MMIO traps when injecting IPI to N target harts
hence IPIs based on IMSIC software injected MSI is slow compared
to the SBI IPI extension.
Add a kernel parameter to disable IPIs in IMSIC driver for platforms
with trap-n-emulated IMSIC.
Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
drivers/irqchip/irq-riscv-imsic-early.c | 12 ++++++++++++
2 files changed, 19 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f1f2c0874da9..7f0e12d0d260 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2538,6 +2538,13 @@
requires the kernel to be built with
CONFIG_ARM64_PSEUDO_NMI.
+ irqchip.riscv_imsic_noipi
+ [RISC-V,EARLY]
+ Force the kernel to not use IMSIC software injected MSIs
+ as IPIs. Intended for system where IMSIC is trap-n-emulated,
+ and thus want to reduce MMIO traps when triggering IPIs
+ to multiple harts.
+
irqfixup [HW]
When an interrupt is not handled search all handlers
for it. Intended to get systems with badly broken
diff --git a/drivers/irqchip/irq-riscv-imsic-early.c b/drivers/irqchip/irq-riscv-imsic-early.c
index 1dbc41d7fe80..c6fba92dd5a9 100644
--- a/drivers/irqchip/irq-riscv-imsic-early.c
+++ b/drivers/irqchip/irq-riscv-imsic-early.c
@@ -9,6 +9,7 @@
#include <linux/cpu.h>
#include <linux/export.h>
#include <linux/interrupt.h>
+#include <linux/init.h>
#include <linux/io.h>
#include <linux/irq.h>
#include <linux/irqchip.h>
@@ -22,6 +23,14 @@
#include "irq-riscv-imsic-state.h"
static int imsic_parent_irq;
+static bool imsic_noipi;
+
+static int __init imsic_noipi_cfg(char *buf)
+{
+ imsic_noipi = true;
+ return 0;
+}
+early_param("irqchip.riscv_imsic_noipi", imsic_noipi_cfg);
#ifdef CONFIG_SMP
static void imsic_ipi_send(unsigned int cpu)
@@ -47,6 +56,9 @@ static int __init imsic_ipi_domain_init(void)
{
int virq;
+ if (imsic_noipi)
+ return 0;
+
/* Create IMSIC IPI multiplexing */
virq = ipi_mux_create(IMSIC_NR_IPI, imsic_ipi_send);
if (virq <= 0)
--
2.43.0
